DS2484 Single-Channel 1-Wire Master with Adjustable Timing and Sleep Mode General Description

DS2484
Single-Channel 1-Wire Master
with Adjustable Timing and Sleep Mode
General Description
The DS2484 is an I2C-to-1-WireM bridge device that
interfaces directly to standard (100kHz max) or fast
(400kHz max) I2C masters to perform protocol conversion between the I2C master and any downstream
1-Wire slave devices. Relative to any attached 1-Wire
slave device, the DS2484 is a 1-Wire master. Internal,
user-adjustable timers relieve the system host processor
from generating time-critical 1-Wire waveforms, supporting both standard and overdrive 1-Wire communication
speeds. In addition, the 1-Wire bus can be powered
down under software control. The dual-voltage operation
allows different operating voltages on the I2C and 1-Wire
side. Strong pullup features support 1-Wire power delivery to 1-Wire devices such as EEPROMs and sensors.
When not in use, the DS2484 can be put in sleep mode
where power consumption is minimal.
Applications
Printers
Benefits and Features
SI2C Host Interface Supports 100kHz and 400kHz
I2C Communication Speeds
SStandard and Overdrive 1-Wire Communication
Speeds
SAdjustable 1-Wire Timing for tRSTL, tMSP, tW0L,
and tREC0
S1-Wire Port Can Be Powered Down Under
Software Control
SSupports Power-Saving Sleep Mode (SLPZ Pin),
Where the 1-Wire Port is in High Impedance
SI2C Operating Voltages: 1.8V ±5%, 3.3V ±10%, and
5.0V +5/-10%
SBuilt-In Level Translator: 1-Wire Operating Voltage
from 1.8V -5% to 5.0V +5%, Independent of I2C
Voltage
SBuilt-In ESD Protection Level of ±8kV Human
Body Model (HBM) Contact Discharge on IO Pin
S-40NC to +85NC Operating Temperature Range
Medical Instruments
S8-Pin TDFN and 6-Pin SOT23 Packages
Industrial Sensors
Cell Phones
Ordering Information appears at end of data sheet.
Typical Application Circuit
3V
5V
RP*
(I2C PORT)
SDA
SCL
VCC
DS2484
µC
SLPZ
IO
1-Wire BUS
1-Wire
DEVICE #1
1-Wire
DEVICE #2
1-Wire
DEVICE #n
*RP = I2C PULLUP RESISTOR (SEE THE Pullup Resistor RP Sizing SECTION FOR RP SIZING)
1-Wire is a registered trademark of Maxim Integrated Products, Inc.
For related parts and recommended products to use with this part, refer to: www.maximintegrated.com/DS2484.related
For pricing, delivery, and ordering information, please contact Maxim Direct at
1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
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19-6701; Rev 0; 5/13
DS2484
Single-Channel 1-Wire Master
with Adjustable Timing and Sleep Mode
ABSOLUTE MAXIMUM RATINGS
Operating Temperature Range........................... -40NC to +85NC
Junction Temperature......................................................+150NC
Storage Temperature Range............................. -55NC to +125NC
Lead Temperature (soldering, 10s).................................+300NC
Soldering Temperature (reflow).......................................+260NC
Voltage Range on Any Pin Relative to Ground........-0.5V to +6V
Maximum Current into Any Pin............................................20mA
Continuous Power Dissipation (TA = +70NC)
SOT23 (derate 8.7mW/NC above +70NC)..................695.7mW
TDFN (derate 16.7mW/NC above +70NC)................1333.3mW
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(TA = -40NC to +85NC, unless otherwise noted.) (Note 1)
PARAMETER
Supply Voltage
SYMBOL
CONDITIONS
VCI2C
TYP
MAX
UNITS
5.25
V
1.71
VCC
I2C Voltage (Note 2)
MIN
1.8V
1.71
1.8
1.89
3.3V
2.97
3.3
3.63
5V
4.5
5.0
5.25
No communication, VCC = full range
Sleep mode, VCC = 5.25V
300
3.0
VPOR
Sleep mode, VCC = 3.6V
VCC = full range
1-Wire Input High Voltage
VIH1
VCC = full range
1-Wire Input Low Voltage
VIL1
VCC = full range
Supply Current
ICC
Power-On-Reset Trip Point
4
1.0
1.5
V
FA
V
IO PIN: GENERAL DATA
500
815
High range
700
1000
1375
1-Wire Output Low Voltage
VOL1
IOL = 8mA sink current
Active Pullup On-Threshold
VIAPO
VCC = full range
Active Pullup Impedance
1-Wire Output Fall Time (Note 4)
RAPU
tF1
0.2 O
VCC
375
RWPU
tAPU
V
Low range
1-Wire Weak Pullup Resistor
Active Pullup On-Time (Note 3)
0.6 O
VCC
0.6
0.95
V
I
0.2
V
1.2
V
1-Wire time slot
See APU bit description
1-Wire reset standard speed
2.375
2.5
2.625
1-Wire reset overdrive speed
0.475
0.5
0.525
VCC = 1.71V, 4mA load
100
VCC = 3.0V, 4mA load
60
VCC = 4.5V, 4mA load
40
Standard, 10pF < CLOAD < 400pF
0.25
1
Overdrive, 10pF < CLOAD < 400pF
0.05
0.2
Fs
I
Fs
IO PIN: 1-Wire TIMING (Note 5)
Reset Low Time
tRSTL
Reset High Time
tRSTH
Standard
Overdrive
Standard and overdrive
-5%
See
Table 7
+5%
Equal to tRSTL
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Fs
Fs
2
DS2484
Single-Channel 1-Wire Master
with Adjustable Timing and Sleep Mode
ELECTRICAL CHARACTERISTICS (continued)
(TA = -40NC to +85NC, unless otherwise noted.) (Note 1)
PARAMETER
Presence-Detect Sample Time
Sampling for Short and Interrupt
SYMBOL
tMSP
tSI
Write-One/Read Low Time
tW1L
Read Sample Time
tMSR
Write-Zero Low Time
tW0L
Write-Zero Recovery Time
tREC0
1-Wire Time Slot
tSLOT
CONDITIONS
Standard
Overdrive
MIN
TYP
MAX
UNITS
-5%
See
Table 7
+5%
Fs
Standard
7.6
8
8.4
Overdrive
0.71
0.75
0.79
Fs
Standard
7.6
8
8.4
Overdrive (Note 6)
0.71
0.75
0.79
Standard
11.4
12
12.6
Overdrive
1.66
1.75
1.84
-5%
See
Table 7
+5%
Fs
Standard and overdrive
-5%
See
Table 7
+5%
Fs
Standard and overdrive
Equal to tW0L + tREC0
Fs
Standard
Overdrive
Fs
Fs
SLPZ PIN
Low-Level Input Voltage
VIL
VCC = full range
-0.5
+0.5
V
High-Level Input Voltage
VIH
(Note 7)
1.3
VCCACT
V
Input Leakage Current (Note 2)
Wake-Up Time from Sleep Mode
II
tSWUP
VCI2C < 1.89V
6
VCI2C < 3.63V
15
VCI2C < 5.25V
32
(Notes 4, 8)
2
ms
-0.5
0.3 O
VCI2C
V
0.7 O
VCI2C
VCI2C +
0.5V
V
FA
I2C SCL AND SDA PINS (Note 9)
Low-Level Input Voltage
VIL
High-Level Input Voltage
VIH
Hysteresis of Schmitt Trigger
Inputs (Note 4)
VHYS
Low-Level Output Voltage at
3mA Sink Current
VOL
Output Fall Time from VIH(MIN) to
VIL(MAX) with a Bus Capacitance
from 10pF to 400pF
tOF
Pulse Width of Spikes
Suppressed by Input Filter
tSP
VCI2C = full range
VCI2C > 2.0V
0.05 O
VCI2C
VCI2C < 2.0V
0.1 O
VCI2C
V
VCI2C > 2.0V
0.4
VCI2C < 2.0V
0.2 O
VCI2C
V
250
ns
50
ns
(Note 4)
60
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DS2484
Single-Channel 1-Wire Master
with Adjustable Timing and Sleep Mode
ELECTRICAL CHARACTERISTICS (continued)
(TA = -40NC to +85NC, unless otherwise noted.) (Note 1)
PARAMETER
SYMBOL
Input Current with Input Voltage
Between 0.1 O VCC(MAX) and 0.9
O VCC(MAX)
II
(Note 10)
Input Capacitance
CI
(Note 4)
SCL Clock Frequency
CONDITIONS
MIN
-10
TYP
MAX
UNITS
+10
FA
10
pF
400
kHz
fSCL
0
tHD:STA
0.6
Fs
Low Period of the SCL Clock
tLOW
1.3
Fs
High Period of the SCL Clock
tHIGH
0.6
Fs
Setup Time for a Repeated
START Condition
tSU:STA
0.6
Fs
Data Hold Time
tHD:DAT
(Notes 11, 12)
Data Setup Time
tSU:DAT
(Note 13)
250
ns
Setup Time for STOP Condition
tSU:STO
0.6
Fs
Bus Free Time Between a STOP
and START Condition
tBUF
1.3
Fs
Hold Time (Repeated) START
Condition (After this period, the
first clock pulse is generated.)
Capacitive Load for Each Bus
Line
Oscillator Warmup Time
0.9
Fs
CB
(Notes 4, 14)
400
pF
tOSCWUP
(Notes 4, 8)
2
ms
Note 1: Limits are 100% production tested at TA = +25°C. Limits over the operating temperature range and relevant supply voltage range are guaranteed by design and characterization. Typical values are at +25°C.
Note 2: The VCI2C voltage is applied at the SLPZ pin. VCI2C must always be < VCC. The DS2484 measures VCI2C after tSWUP
(wakeup from sleep mode) or after tOSCWUP (power-on reset). The Device Reset command does not cause the DS2484 to
measure VCI2C.
Note 3: The active pullup does not apply to the rising edge of a presence pulse outside of a 1-Wire Reset command or during the
recovery after a short on the 1-Wire line.
Note 4: Guaranteed design and not production tested.
Note 5: Except for tF1, all 1-Wire timing specifications are derived from the same timing circuit.
Note 6: Although 1-Wire slave data sheets specify a tW1L and tRL minimum of 1µs, 1-Wire slaves will accept the shorter 0.71µs
tW1L and tRL of the DS2484.
Note 7: VCCACT refers to the VCC level being applied in the application.
Note 8: I2C communication should not take place for the max tOSCWUP or tSWUP time following a power-on reset or a wake-up
from sleep mode.
Note 9: All I2C timing values are referenced to VIH(MIN) and VIL(MAX) levels.
Note 10:The DS2484 does not obstruct the SDA and SCL lines if SLPZ is at 0V or if VCC is switched off.
Note 11:The DS2484 provides a hold time of at least 300ns for the SDA signal (referenced to the VIH(MIN) of the SCL signal) to
bridge the undefined region of the falling edge of SCL.
Note 12:The maximum tHD:DAT must only be met if the device does not stretch the low period (tLOW) of the SCL signal.
Note 13:A fast mode I2C bus device can be used in a standard mode I2C bus system, but the requirement tSU:DAT R 250ns
must then be met. This requirement is met since the DS2484 does not stretch the low period of the SCL signal. Also the
acknowledge timing must meet this setup time (I2C bus specification Rev. 03, 19 June 2007).
Note 14:CB = Total capacitance of one bus line in pF. The maximum bus capacitance allowable can vary from this value depending on the actual operating voltage and frequency of the application (I2C bus specification Rev. 03, 19 June 2007).
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DS2484
Single-Channel 1-Wire Master
with Adjustable Timing and Sleep Mode
Pin Configurations
TOP VIEW
SDA
2
SLPZ
N.C.
DS2484
3
EP
4
8
GND
7
IO
6
VCC
5
N.C.
+
1
+
SCL
TOP MARK
TDFN
(2mm x 3mm)
2484
YMrr
TOP VIEW
TOP MARK
VCC
IO
GND
6
5
4
SOT23
3Hrr
+
+
DS2484
1
2
3
SLPZ
SDA
SCL
“rr” = REVISION CODE
Pin Description
PIN
NAME
FUNCTION
TDFN-EP
SOT23
1
3
SCL
I2C Serial-Clock Input. Must be connected to the I2C bus supply voltage through a pullup
resistor.
2
2
SDA
I2C Serial-Data Input/Output. Must be connected to the I2C bus supply voltage through a
pullup resistor.
3
1
SLPZ
Power Supply for I2C Port and Active-Low Control Input to Activate the Low-Power Sleep
Mode. This pin can be driven directly by a push-pull port or by an open-drain port with a
2.2kI pullup resistor to the I2C voltage (VCI2C) over the entire operating voltage range.
4, 5
—
N.C.
No Connection. Not internally connected.
6
6
VCC
Power-Supply Input
7
5
IO
8
4
GND
—
—
EP
Input/Output Driver for 1-Wire Line
Ground Reference
Exposed Pad (TDFN Only). Solder evenly to the board’s ground plane for proper operation.
Refer to Application Note 3273: Exposed Pads: A Brief Introduction for additional information.
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DS2484
Single-Channel 1-Wire Master
with Adjustable Timing and Sleep Mode
VCC
CONFIGURATION AND
TIMING REGISTER
INPUT/OUTPUT
CONTROLLER
I2C
INTERFACE
CONTROLLER
SDA
SCL
T-TIME OSC
SLPZ
STATUS
REGISTER
GND
READ DATA
REGISTER
LINE
XCVR
IO
DS2484
Figure 1. Block Diagram
Table 1. Device Configuration Register Bit Assignment
BIT 7
BIT 6
1WS
SPU
BIT 5
PDN
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
APU
1WS
SPU
PDN
APU
Detailed Description
The DS2484 is a self-timed 1-Wire master that supports
advanced 1-Wire waveform features including standard
and overdrive speeds, active pullup, and strong pullup
for power delivery. The active pullup affects rising edges
on the 1-Wire side. The strong pullup function uses the
same pullup transistor as the active pullup, but with a
different control algorithm. Once supplied with command
and data, the input/output controller of the DS2484 performs time-critical 1-Wire communication functions such
as reset/presence-detect cycle, read-byte, write-byte,
single bit R/W, and triplet for ROM Search, without requiring interaction with the host processor. The host obtains
feedback (completion of a 1-Wire function, presence
pulse, 1-Wire short, search direction taken) through the
Status register and data through the Read Data register. The DS2484 communicates with a host processor
through its I2C bus interface in standard mode or in fast
mode. See Figure 1 for a block diagram.
Device Registers
The DS2484 has four registers that the I2C host can
read: Device Configuration, Status, Read Data, and Port
Configuration. These registers are addressed by a read
pointer. The position of the read pointer, i.e., the register that the host reads in a subsequent read access,
is defined by the instruction the DS2484 executed last.
To enable certain 1-Wire features, the host has readand write-access to the Device Configuration and Port
Configuration registers.
Device Configuration Register
The DS2484 supports four 1-Wire features that are
enabled or selected through the Device Configuration
register (Table 1). These features are as follows:
• Active Pullup (APU)
• 1-Wire Power-Down (PDN)
• Strong Pullup (SPU)
• 1-Wire Speed (1WS)
APU, SPU, and 1WS can be selected in any combination.
While APU and 1WS maintain their states, SPU returns to
its inactive state as soon as the strong pullup has ended.
After a device reset (power-up cycle or initiated by the
Device Reset command), the Device Configuration register reads 00h. When writing to the Device Configuration
register, the new data is accepted only if the upper nibble
(bits 7 to 4) is the one’s complement of the lower nibble
(bits 3 to 0). When read, the upper nibble is always 0h.
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DS2484
Single-Channel 1-Wire Master
with Adjustable Timing and Sleep Mode
Active Pullup (APU)
The APU bit controls whether an active pullup (low
impedance transistor) or a passive pullup (RWPU resistor) is used to drive a 1-Wire line from low to high. When
APU = 0, active pullup is disabled (resistor mode).
Enabling active pullup is generally recommended for
best 1-Wire bus performance. The active pullup does
not apply to the rising edge of a recovery after a short
on the 1-Wire line. If enabled, a fixed-duration active
pullup (typically 2.5Fs standard speed, 0.5Fs overdrive
speed) also applies in a reset/presence detect cycle on
the rising edges after tRSTL and after tPDL.
The circuit that controls rising edges operates as follows
(Figure 2): At t1, the pulldown (from DS2484 or 1-Wire
slave) ends. From this point on the 1-Wire bus is pulled
high through RWPU internal to the DS2484. VCC and the
capacitive load of the 1-Wire line determine the slope. In
case that active pullup is disabled (APU = 0), the resistive pullup continues, as represented by the solid line.
With active pullup enabled (APU = 1), and when at t2 the
voltage has reached the VIAPO threshold, the DS2484
activates a low-impedance pullup transistor, as represented by the dashed line. The active pullup remains
active until the end of the time slot (t3), after which the
resistive pullup continues. The shortest duration of the
active pullup is tREC0 - (t2 - t1) in a write-zero time slot
and the longest duration is tW0L + tREC0 - tW1L - (t2 - t1)
in a write-one time slot. In a read-data time slot, the active
pullup duration is slave dependent. See the Strong Pullup
(SPU) section for a way to keep the pullup transistor conducting beyond t3.
1-Wire Power Down (PDN)
The PDN bit is used to remove power from the 1-Wire
port, e.g., to force a 1-Wire slave to perform a power-on
reset. PDN can as well be used in conjunction with the
sleep mode (see Table 2 for details). While PDN is 1,
no 1-Wire communication is possible. To end the 1-Wire
power-down state, the PDN bit must be changed to 0.
Writing both the PDN bit and the SPU bit to 1 forces the
SPU bit to 0. With the DS2483, both bits can be written
to 1, which can be used to logically distinguish between
both parts.
Table 2. Effects of PDN and SLPZ
PDN =
SLPZ IS LOGIC 0
SLPZ IS LOGIC 1
0
•
•
•
RWPU is connected.
IO is at VCC, keeping the slaves powered.
The DS2484 is powered down (sleep mode).
•
•
•
RWPU is connected.
IO is at VCC, keeping the slaves powered.
The DS2484 is powered up (normal operation).
1
•
•
•
RWPU is disconnected.
IO is at 0V, causing the slaves to lose power.
The DS2484 is powered down (sleep mode).
•
•
•
RWPU is disconnected.
IO is at 0V, causing the slaves to lose power.
The DS2484 is powered up.
VCC
APU = 1
NEXT TIME SLOT
APU = 0
VIAPO
VIL1MAX
0V
1-Wire BUS IS
DISCHARGED
tREC0
t1
t2
t3
Figure 2. Rising Edge Pullup as Seen at the End of a Write-Zero Time Slot
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DS2484
Single-Channel 1-Wire Master
with Adjustable Timing and Sleep Mode
case), the SPU bit in the Device Configuration register
is written to 0, or the DS2484 receives the Device Reset
command. When the strong pullup ends, the SPU bit is
automatically reset to 0. Using the strong pullup feature
does not change the state of the APU bit in the Device
Configuration register.
Strong Pullup (SPU)
The SPU bit is used to activate the strong pullup function prior to a 1-Wire Write Byte or 1-Wire Single Bit
command. Strong pullup is commonly used with 1-Wire
EEPROM devices when copying scratchpad data to the
main memory or when performing a SHA computation
and with parasitically powered temperature sensors or
A/D converters. The respective Maxim 1-Wire IC data
sheets specify the location in the communications protocol after which the strong pullup should be applied. The
SPU bit must be set immediately prior to issuing the command that puts the 1-Wire device into the state where it
needs the extra power. The strong pullup uses the same
internal pullup transistor as the active pullup feature.
See the RAPU parameter in the Electrical Characteristics
to determine whether the voltage drop is low enough to
maintain the required 1-Wire voltage at a given load current and 1-Wire supply voltage.
1-Wire Speed (1WS)
The 1WS bit determines the timing of any 1-Wire communication generated by the DS2484. All 1-Wire slave
devices support standard speed (1WS = 0). Many
1-Wire devices can also communicate at a higher data
rate, called overdrive speed. To change from standard
to overdrive speed, a 1-Wire device needs to receive
an Overdrive-Skip ROM or Overdrive-Match ROM command, as explained in the Maxim 1-Wire IC data sheets.
The change in speed occurs immediately after the 1-Wire
device has received the speed-changing command
code. The DS2484 must take part in this speed change
to stay synchronized. This is accomplished by writing to
the Device Configuration register with the 1WS bit as 1
immediately after the 1-Wire Byte command that changes
the speed of a 1-Wire device. Writing to the Device
Configuration register with the 1WS bit as 0, followed by
a 1-Wire Reset command, changes the DS2484 and any
1-Wire devices on the active 1-Wire line back to standard
speed.
If SPU is 1 and APU is 0, the DS2484 treats the rising
edge of the time slot as if the active pullup was activated, but uses VIH1 as the threshold to enable the strong
pullup. If SPU is 1 and APU is 1, the threshold voltage
to enable the strong pullup is VIAPO. Once enabled, in
contrast to the active pullup, the internal pullup transistor remains conducting, as shown in Figure 3, until one
of three events occurs: the DS2484 receives a command that generates 1-Wire communication (the typical
LAST BIT OF 1-Wire WRITE BYTE OR 1-Wire SINGLE BIT FUNCTION
VCC
WRITE-ONE CASE
NEXT
TIME SLOT
OR 1-Wire
RESET
SEE TEXT
WRITE-ZERO CASE
0V
tSLOT
DS2484 RESISTIVE PULLUP
DS2484 PULLDOWN
DS2484 STRONG PULLUP
Figure 3. Low-Impedance Pullup Timing
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DS2484
Single-Channel 1-Wire Master
with Adjustable Timing and Sleep Mode
Table 3. Status Register Bit Assignment
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
DIR
TSB
SBR
RST
LL
SD
PPD
1WB
Status Register
The read-only Status register is the general means for
the DS2484 to report bit-type data from the 1-Wire side,
1-Wire busy status, and its own reset status to the host
processor (Table 3). All 1-Wire communication commands and the Device Reset command position the read
pointer at the Status register for the host processor to
read with minimal protocol overhead. Status information
is updated during the execution of certain commands
only. Bit details are given in the following descriptions.
1-Wire Busy (1WB)
The 1WB bit reports to the host processor whether the
1-Wire line is busy. During 1-Wire communication 1WB
is 1; once the command is completed, 1WB returns to
its default 0. Details on when 1WB changes state and
for how long it remains at 1 are found in the Function
Commands section.
Presence-Pulse Detect (PPD)
The PPD bit is updated with every 1-Wire Reset command. If the DS2484 detects a presence pulse from a
1-Wire device at tMSP during the presence-detect cycle,
the PPD bit is set to 1. This bit returns to its default 0 if
there is no presence pulse or if the 1-Wire line is shorted
during a subsequent 1-Wire Reset command.
Short Detected (SD)
The SD bit is updated with every 1-Wire Reset command. If the DS2484 detects a logic 0 on the 1-Wire line
at tSI during the presence-detect cycle, the SD bit is set
to 1. This bit returns to its default 0 with a subsequent
1-Wire Reset command, provided that the short has been
removed. If SD is 1, PPD is 0. The DS2484 cannot distinguish between a short and a DS1994 or DS2404 signaling a 1-Wire interrupt. For this reason, if a DS2404 or
DS1994 is used in the application, the interrupt function
must be disabled. The interrupt signaling is explained in
the respective Maxim 1-Wire IC data sheets.
Logic Level (LL)
The LL bit reports the logic state of the active 1-Wire line
without initiating any 1-Wire communication. The 1-Wire
line is sampled for this purpose every time the Status
register is read. The sampling and updating of the LL bit
takes place when the host processor has addressed the
DS2484 in read mode (during the acknowledge cycle),
provided that the read pointer is positioned at the Status
register.
Device Reset (RST)
If the RST bit is 1, the DS2484 has performed an internal
reset cycle, either caused by a power-on reset or from
executing the Device Reset command. The RST bit is
cleared automatically when the DS2484 executes a Write
Device Configuration command to restore the selection
of the desired 1-Wire features.
Single Bit Result (SBR)
The SBR bit reports the logic state of the active 1-Wire
line sampled at tMSR of a 1-Wire Single Bit command or
the first bit of a 1-Wire Triplet command. The power-on
default of SBR is 0. If the 1-Wire Single Bit command
sends a 0 bit, SBR should be 0. With a 1-Wire Triplet
command, SBR could be 0 as well as 1, depending on
the response of the 1-Wire devices connected. The same
result applies to a 1-Wire Single Bit command that sends
a 1 bit.
Triplet Second Bit (TSB)
The TSB bit reports the logic state of the active 1-Wire
line sampled at tMSR of the second bit of a 1-Wire Triplet
command. The power-on default of TSB is 0. This bit is
updated only with a 1-Wire Triplet command and has no
function with other commands.
Branch Direction Taken (DIR)
Whenever a 1-Wire Triplet command is executed, this bit
reports to the host processor the search direction that
was chosen by the third bit of the triplet. The power-on
default of DIR is 0. This bit is updated only with a 1-Wire
Triplet command and has no function with other commands. For additional information, see the description of
the 1-Wire Triplet command and Application Note 187:
1-Wire Search Algorithm.
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DS2484
Single-Channel 1-Wire Master
with Adjustable Timing and Sleep Mode
Table 4. Port Configuration Register Bit Assignment
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
0
0
0
0
VAL3
VAL2
VAL1
VAL0
VAL[3:0]: Parameter Value Code
See Table 7 for the conversion between binary code and parameter value.
BITS 3:0
Port Configuration Register
Function Commands
Parameter 000 (tRSTL) standard speed, overdrive speed
Parameter 001 (tMSP) standard speed, overdrive speed
Parameter 010 (tW0L) standard speed, overdrive speed
Parameter 011 (tREC0)
Parameter 100 (RWPU)
The DS2484 understands nine function commands that
fall into four categories: device control, I2C communication, 1-Wire setup, and 1-Wire communication. The
feedback path to the host is controlled by a read pointer,
which is set automatically by each function command
for the host to efficiently access relevant information.
The host processor sends these commands and applicable parameters as strings of 1 or 2 bytes using the
I2C interface. The I2C protocol requires that each byte
be acknowledged by the receiving party to confirm
acceptance or not be acknowledged to indicate an error
condition (invalid code or parameter) or to end the communication. See the I2C Interface section for details of
the I2C protocol including acknowledge.
The Port Configuration register allows verifying the settings for the 1-Wire port (Table 4). The Adjust 1-Wire
Port command positions the read pointer to the Port
Configuration register for the host processor to read
with minimal protocol overhead. When reading the Port
Configuration register, the parameter values are reported
in this sequence:
If one continues reading, the parameter number rolls
over to 000 and one receives the same data again.
Note that the upper 4 bits read from the port configuration register are always 0. See Table 7 for the conversion
between parameter value code and actual parameter
value.
The function commands are as follows:
1) Device Reset
2) Set Read Pointer
3) Write Device Configuration
4) Adjust 1-Wire Port
5) 1-Wire Reset
6) 1-Wire Single Bit
7) 1-Wire Write Byte
8) 1-Wire Read Byte
9) 1-Wire Triplet
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DS2484
Single-Channel 1-Wire Master
with Adjustable Timing and Sleep Mode
Device Reset
Command Code
F0h
Command Parameter
None
Description
Performs a global reset of device state machine logic. Terminates any ongoing 1-Wire
communication.
Typical Use
Device initialization after power-up; reinitialization (reset) as desired.
Restriction
None (can be executed at any time)
Error Response
None
Command Duration
Maximum 525ns. Counted from falling SCL edge of the command code acknowledge bit.
1-Wire Activity
Ends maximum 262.5ns after the falling SCL edge of the command code acknowledge bit.
Read Pointer Position
Status register (for busy polling).
Status Bits Affected
RST set to 1; 1WB, PPD, SD, SBR, TSB, DIR set to 0.
Device Configurations Affected
1WS, APU, PDN, SPU set to 0.
Port Configurations Affected
tRSTL, tMSP, tW0L, tREC0, and RWPU default values apply.
Set Read Pointer
Command Code
E1h
Command Parameter
Pointer Code (see Table 5)
Description
Sets the read pointer to the specified register. Overwrites the read pointer position of any
1-Wire communication command in progress.
Typical Use
To prepare reading the result from a 1-Wire Read Byte command; random read access of
registers.
Restriction
None (can be executed at any time).
Error Response
If the pointer code is not valid, the pointer code is not acknowledged and the command is
ignored.
Command Duration
None. The read pointer is updated on the rising SCL edge of the pointer code acknowledge bit.
1-Wire Activity
Not affected.
Read Pointer Position
As specified by the pointer code.
Status Bits Affected
None
Device Configurations Affected
None
Port Configurations Affected
None
Table 5. Valid Read Pointer Codes
REGISTER
CODE
Device Configuration Register
C3h
Status Register
F0h
Read Data Register
E1h
Port Configuration Register
B4h
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DS2484
Single-Channel 1-Wire Master
with Adjustable Timing and Sleep Mode
Write Device Configuration
Command Code
D2h
Command Parameter
Configuration Byte
Description
Writes a new device configuration byte. The new settings take effect immediately. Note:
When writing to the Device Configuration register, the new data is accepted only if the upper
nibble (bits 7 to 4) is the one’s complement of the lower nibble (bits 3 to 0). When read, the
upper nibble is always 0h.
Typical Use
Defining the features for subsequent 1-Wire communication.
Restriction
1-Wire activity must have ended before the DS2484 can process this command.
Error Response
Command code and parameter are not acknowledged if 1WB = 1 at the time the command
code is received and the command is ignored.
Command Duration
None. The Device Configuration register is updated on the rising SCL edge of the
configuration-byte acknowledge bit.
1-Wire Activity
None
Read Pointer Position
Device Configuration register (to verify write).
Status Bits Affected
RST set to 0.
Device Configurations Affected
1WS, SPU, PDN, APU updated.
Port Configurations Affected
None
Adjust 1-Wire Port
Command Code
C3h
Command Parameter
Control Byte
Description
Updates the selected 1-Wire port parameter, which affects the 1-Wire timing or pullup
resistor selection. See Table 6 for the control byte format. Note: Upon a power-on reset or
after a Device Reset command, the parameter default values apply.
Typical Use
To adapt the 1-Wire port to the needs of the application. This can be necessary to
accommodate the slave timing requirements, which are different at lower pullup voltage.
Restriction
1-Wire activity must have ended before this command can be processed.
Error Response
Command code and data byte are not acknowledged if 1WB = 1 at the time the command
code is received and the command is ignored.
Command Duration
None. The selected port parameter is updated on the rising SCL edge of the control-byte
acknowledge bit.
1-Wire Activity
None
Read Pointer Position
Port Configuration register (for verification).
Status Bits Affected
None
Device Configurations Affected
None
Port Configurations Affected
As specified by the control byte.
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DS2484
Single-Channel 1-Wire Master
with Adjustable Timing and Sleep Mode
Table 6. Bit Allocation in the Control Byte
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
P2
P1
P0
OD
VAL3
VAL2
VAL1
VAL0
BITS 7:5
P[2:0]: Parameter Selection
000: selects tRSTL
001: selects tMSP
010: selects tW0L
011: selects tREC0; the OD flag does not apply (don’t care)
100: selects RWPU; the OD flag does not apply (don’t care)
BIT 4
OD: Overdrive Control
0: the value provided applies to the standard speed setting
1: the value provided applies to the overdrive speed setting
VAL[3:0]: Parameter Value Code
See Table 7 for the conversion between binary code and parameter value.
BITS 3:0
Table 7. Conversion Between Parameter Code and Typical Parameter Value
PARAMETER
VALUE
CODE
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
PARAMETER 000
tRSTL (µs)
PARAMETER 001
tMSP (µs)
PARAMETER 010
tW0L (µs)
OD = 0
440
460
480
500
520
540
560
580
600
620
640
660
680
700
720
740
OD = 0
58
58
60
62
64
66
68
70
72
74
76
76
76
76
76
76
OD = 0
52
54
56
58
60
62
64
66
68
70
70
70
70
70
70
70
OD = 1
44
46
48
50
52
54
56
58
60
62
64
66
68
70
72
74
OD = 1
5.5
5.5
6.0
6.5
7.0
7.5
8.0
8.5
9.0
9.5
10.0
10.5
11.0
11.0
11.0
11.0
OD = 1
5.0
5.5
6.0
6.5
7.0
7.5
8.0
8.5
9.0
9.5
10
10
10
10
10
10
PARAMETER 011
tREC0 (µs)
PARAMETER 100
RWPU (W)
OD = N/A
2.75
2.75
2.75
2.75
2.75
2.75
5.25
7.75
10.25
12.75
15.25
17.75
20.25
22.75
25.25
25.25
OD = N/A
500
500
500
500
500
500
1000
1000
1000
1000
1000
1000
1000
1000
1000
1000
Note: The power-on default values are bold.
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DS2484
Single-Channel 1-Wire Master
with Adjustable Timing and Sleep Mode
1-Wire Reset
Command Code
B4h
Command Parameter
None
Description
Generates a 1-Wire reset/presence-detect cycle at the 1-Wire line (Figure 4). The state of
the 1-Wire line is sampled at tSI and tMSP and the result is reported to the host processor
through the Status register bits PPD and SD.
Typical Use
To initiate or end any 1-Wire communication sequence.
Restriction
1-Wire activity must have ended before the DS2484 can process this command.
Error Response
Command code is not acknowledged if 1WB = 1 at the time the command code is received
and the command is ignored.
Command Duration
2 O tRSTL + maximum 262.5ns, counted from the falling SCL edge of the command code
acknowledge bit.
1-Wire Activity
Begins maximum 262.5ns after the falling SCL edge of the command code acknowledge bit.
Read Pointer Position
Status register (for busy polling).
Status Bits Affected
Device Configurations Affected
1WB (set to 1 for 2 O tRSTL), PPD is updated at tRSTL + tMSP, SD is updated at tRSTL + tSI.
1WS, APU apply.
Port Configurations Affected
tRSTL, tMSP, tW0L, tREC0, and RWPU current values apply.
RESET PULSE
PRESENCE/SHORT DETECT
tMSP
tSI
VCC
APU CONTROLLED
EDGE
VIH1
VIL1
0V
tF1
PRESENCE PULSE
tRSTL
PULLUP (SEE FIGURE 2)
tRSTH
DS2484 PULLDOWN
1-Wire SLAVE PULLDOWN
Figure 4. 1-Wire Reset/Presence-Detect Cycle
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DS2484
Single-Channel 1-Wire Master
with Adjustable Timing and Sleep Mode
1-Wire Single Bit
Command Code
87h
Command Parameter
Bit Byte
Description
Generates a single 1-Wire time slot with a bit value “V” as specified by the bit byte at the
1-Wire line (Table 8). A V value of 0b generates a write-zero time slot (Figure 5); a V value of
1b generates a write-one time slot, which also functions as a read-data time slot (Figure 6). In
either case, the logic level at the 1-Wire line is tested at tMSR and SBR is updated.
Typical Use
To perform single-bit writes or reads at the 1-Wire line when single bit communication is
necessary (the exception).
Restriction
1-Wire activity must have ended before the DS2484 can process this command.
Error Response
Command code and bit byte are not acknowledged if 1WB = 1 at the time the command
code is received and the command is ignored.
Command Duration
tSLOT + maximum 262.5ns, counted from the falling SCL edge of the first bit (MSB) of the bit
byte.
1-Wire Activity
Begins maximum 262.5ns after the falling SCL edge of the MSB of the bit byte.
Read Pointer Position
Status register (for busy polling and data reading).
Status Bits Affected
1WB (set to 1 for tSLOT), SBR is updated at tMSR, DIR (may change its state).
Device Configurations Affected
1WS, APU, SPU apply.
Port Configurations Affected
tRSTL, tMSP, tW0L, tREC0, and RWPU current values apply.
Table 8. Bit Allocation in the Bit Byte
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
V
X
X
X
X
X
X
X
X = Don’t care
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DS2484
Single-Channel 1-Wire Master
with Adjustable Timing and Sleep Mode
tWOL
tMSR
VCC
VIH1
VIL1
0V
tF1
tREC0
tSLOT
PULLUP (SEE FIGURE 2)
DS2484 PULLDOWN
Figure 5. Write-Zero Time Slot
tMSR
tW1L
VCC
VIH1
VIL1
0V
tF1
tSLOT
PULLUP (SEE FIGURE 2)
DS2484 PULLDOWN
1-Wire SLAVE PULLDOWN
NOTE: DEPENDING ON ITS INTERNAL STATE, A 1-Wire SLAVE DEVICE TRANSMITS DATA TO ITS MASTER (e.g., THE DS2484). WHEN RESPONDING WITH A 0,
A 1-Wire SLAVE STARTS PULLING THE LINE LOW DURING tW1L. ITS INTERNAL TIMING GENERATOR DETERMINES WHEN THIS PULLDOWN ENDS AND THE VOLTAGE
STARTS RISING AGAIN. WHEN RESPONDING WITH A 1, A 1-Wire SLAVE DOES NOT HOLD THE LINE LOW AT ALL, AND THE VOLTAGE STARTS RISING AS SOON AS tW1L
IS OVER. 1-Wire DEVICE DATA SHEETS USE THE TERM tRL INSTEAD OF tW1L TO DESCRIBE A READ-DATA TIME SLOT. TECHNICALLY, tRL AND tW1L HAVE IDENTICAL
SPECIFICATIONS AND CANNOT BE DISTINGUISHED FROM EACH OTHER.
Figure 6. Write-One and Read-Data Time Slot
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DS2484
Single-Channel 1-Wire Master
with Adjustable Timing and Sleep Mode
1-Wire Write Byte
Command Code
A5h
Command Parameter
Data Byte
Description
Writes a single data byte to the 1-Wire line.
Typical Use
To write commands or data to the 1-Wire line. Equivalent to executing eight 1-Wire Single Bit
commands, but faster due to less I2C traffic.
Restriction
1-Wire activity must have ended before the DS2484 can process this command.
Error Response
Command code and data byte are not acknowledged if 1WB = 1 at the time the command
code is received and the command is ignored.
Command Duration
8 x tSLOT + maximum 262.5ns, counted from falling edge of the last bit (LSB) of the data
byte.
1-Wire Activity
Begins maximum 262.5ns after falling SCL edge of the LSB of the data byte (i.e., before the
data-byte acknowledge). Note: The bit order on the I2C bus and the 1-Wire line is different
(1-Wire: LSB first; I2C: MSB first). Therefore, 1-Wire activity cannot begin before the DS2484
has received the full data byte.
Read Pointer Position
Status register (for busy polling).
Status Bits Affected
1WB (set to 1 for 8 x tSLOT).
Device Configurations Affected
1WS, SPU, APU apply.
Port Configurations Affected
tRSTL, tMSP, tW0L, tREC0, and RWPU current values apply.
1-Wire Read Byte
Command Code
96h
Command Parameter
None
Description
Generates eight read-data time slots on the 1-Wire line and stores result in the Read Data
register.
Typical Use
To read data from the 1-Wire line. Equivalent to executing eight 1-Wire Single Bit commands
with V = 1 (write-one time slot), but faster due to less I2C traffic.
Restriction
1-Wire activity must have ended before the DS2484 can process this command.
Error Response
Command code is not acknowledged if 1WB = 1 at the time the command code is received
and the command is ignored.
Command Duration
8 x tSLOT + maximum 262.5ns, counted from the falling SCL edge of the command code
acknowledge bit.
1-Wire Activity
Begins maximum 262.5ns after the falling SCL edge of the command code acknowledge bit.
Read Pointer Position
Status register (for busy polling). Note: To read the data byte received from the 1-Wire line,
issue the Set Read Pointer command and select the Read Data register. Then access the
DS2484 in read mode.
Device Configurations Affected
1WB (set to 1 for 8 x tSLOT).
1WS, APU apply.
Port Configurations Affected
tRSTL, tMSP, tW0L, tREC0, and RWPU current values apply.
Status Bits Affected
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DS2484
Single-Channel 1-Wire Master
with Adjustable Timing and Sleep Mode
1-Wire Triplet
Command Code
78h
Command Parameter
Direction Byte
Description
Generates three time slots: two read time slots and one write time slot at the 1-Wire line.
The type of write time slot depends on the result of the read time slots and the direction
byte. The direction byte determines the type of write time slot if both read time slots are 0 (a
typical case). In this case, the DS2484 generates a write-one time slot if V = 1 and a writezero time slot if V = 0. See Table 9.
If the read time slots are 0 and 1, they are followed by a write-zero time slot.
If the read time slots are 1 and 0, they are followed by a write-one time slot.
If the read time slots are both 1 (error case), the subsequent write time slot is a write-one.
Typical Use
To perform a 1-Wire Search ROM sequence; a full sequence requires this command to be
executed 64 times to identify and address one device.
Restriction
1-Wire activity must have ended before the DS2484 can process this command.
Error Response
Command code and direction byte is not acknowledged if 1WB = 1 at the time the
command code is received and the command is ignored.
Command Duration
3 x tSLOT + maximum 262.5ns, counted from the falling SCL edge of the first bit (MSB) of the
direction byte.
1-Wire Activity
Begins maximum 262.5ns after the falling SCL edge of the MSB of the direction byte.
Read Pointer Position
Status Register (for busy polling).
Status Bits Affected
1WB (set to 1 for 3 x tSLOT), SBR is updated at the first tMSR, TSB and DIR are updated at
the second tMSR (i.e., at tSLOT + tMSR).
Device Configurations Affected
1WS, APU apply.
Port Configurations Affected
tRSTL, tMSP, tW0L, tREC0, and RWPU current values apply.
Table 9. Bit Allocation in the Direction Byte
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
V
X
X
X
X
X
X
X
X = Don’t care
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18
DS2484
Single-Channel 1-Wire Master
with Adjustable Timing and Sleep Mode
MSB FIRST
MSB
LSB
MSB
LSB
SDA
SLAVE
ADDRESS
SCL
R/W
1–7
IDLE
ACK
8
9
START
CONDITION
DATA
1–7
ACK
8
REPEATED IF MORE BYTES
ARE TRANSFERRED
9
DATA
1–7
ACK/
NACK
8
9
STOP CONDITION
REPEATED START
Figure 7. I2C Protocol Overview
7-BIT SLAVE ADDRESS
A6
A5
A4
A3
A2
A1
A0
0
0
1
1
0
0
0
R/W
DETERMINES
READ OR WRITE
MSB
Figure 8. DS2484 Slave Address
I2C Interface
General Characteristics
The I2C bus uses a data line (SDA) and a clock signal
(SCL) for communication. Both SDA and SCL are bidirectional lines connected to a positive supply voltage
through a pullup resistor. When there is no communication, both lines are high. The output stages of devices
connected to the bus must have an open drain or open
collector to perform the wired-AND function. Data on the
I2C bus can be transferred at rates of up to 100kbps in
standard mode and up to 400kbps in fast mode. The
DS2484 works in both modes.
A device that sends data on the bus is defined as a
transmitter, and a device receiving data is defined as a
receiver. The device that controls the communication is
called a master. The devices that are controlled by the
master are slaves. To be individually accessed, each
device must have a slave address that does not conflict
with other devices on the bus.
Data transfers can be initiated only when the bus is not
busy. The master generates the serial clock (SCL), controls the bus access, generates the START and STOP
conditions, and determines the number of data bytes
transferred between START and STOP (Figure 7). Data
is transferred in bytes with the most significant bit being
transmitted first. After each byte follows an acknowledge
bit to allow synchronization between master and slave.
Slave Address
Figure 8 shows the slave address to which the DS2484
responds. The slave address is part of the slave address/
control byte. The last bit of the slave address/control
byte (R/W) defines the data direction. When set to 0,
subsequent data flows from master to slave (write access
mode); when set to 1, data flows from slave to master
(read access mode).
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DS2484
Single-Channel 1-Wire Master
with Adjustable Timing and Sleep Mode
I2C Definitions
The following terminology is commonly used to describe
I2C data transfers. See Figure 9 for a timing diagram.
Bus Idle or Not Busy: Both SDA and SCL are inactive and in their logic-high states.
START Condition: To initiate communication with a
slave, the master must generate a START condition.
A START condition is defined as a change in state of
SDA from high to low while SCL remains high.
STOP Condition: To end communication with a
slave, the master must generate a STOP condition. A
STOP condition is defined as a change in state of SDA
from low to high while SCL remains high.
Repeated START Condition: Repeated STARTs are
commonly used for read accesses to select a specific
data source or address from which to read. The master can use a repeated START condition at the end
of a data transfer to immediately initiate a new data
transfer following the current one. A repeated START
condition is generated the same way as a normal
START condition, but without leaving the bus idle after
a STOP condition.
Data Valid: With the exception of the START and
STOP condition, transitions of SDA can occur only
during the low state of SCL. The data on SDA must
remain valid and unchanged during the entire high
pulse of SCL plus the required setup and hold time
(tHD:DAT after the falling edge of SCL and tSU:DAT
before the rising edge of SCL; see Figure 9). There is
one clock pulse per bit of data. Data is shifted into the
receiving device during the rising edge of SCL pulse.
When finished with writing, the master must release
the SDA line for a sufficient amount of setup time
(minimum tSU:DAT + tR in Figure 9) before the next rising edge of SCL to start reading. The slave shifts out
each data bit on SDA at the falling edge of the previous SCL pulse and the data bit is valid at the rising
edge of the current SCL pulse. The master generates
all SCL clock pulses, including those needed to read
from a slave.
Acknowledge: Typically a receiving device, when
addressed, is obliged to generate an acknowledge
after the receipt of each byte. The master must
generate a clock pulse that is associated with this
acknowledge bit. A device that acknowledges must
pull SDA low during the acknowledge clock pulse
in such a way that SDA is stable low during the high
period of the acknowledge-related clock pulse plus
the required setup and hold time (tHD:DAT after the
falling edge of SCL and tSU:DAT before the rising
edge of SCL).
SDA
tBUF
tF
tSP
tHD:STA
tLOW
SCL
tHD:STA
tHIGH
tR
tHD:DAT
STOP
START
tSU:STA
SPIKE
SUPPRESSION
tSU:STO
tSU:DAT
REPEATED
START
NOTE: TIMING IS REFERENCED TO VIL(MAX) AND VIH(MIN).
Figure 9. I2C Timing Diagram
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DS2484
Single-Channel 1-Wire Master
with Adjustable Timing and Sleep Mode
Not Acknowledged by Slave: A slave device could
be unable to receive or transmit data, e.g., because
it is busy performing a real-time function or is in
sleep mode. In this case, the slave device does not
acknowledge its slave address and leaves the SDA
line high. A slave device that is ready to communicate
acknowledges at least its slave address. However,
some time later the slave can refuse to accept data,
e.g., because of an invalid command or parameter.
In this case, the slave device does not acknowledge
any of the bytes that it refuses and leaves SDA high.
In either case, after a slave has failed to acknowledge,
the master first should generate a repeated START
condition or a STOP condition followed by a START
condition to begin a new data transfer.
Not Acknowledged by Master: At some time when
receiving data, the master must signal an end of data
to the slave device. To achieve this, the master does
not acknowledge the last byte that it has received
from the slave. In response, the slave releases SDA,
allowing the master to generate the STOP condition.
Writing to the DS2484
To write to the DS2484, the master must access the
device in write mode, i.e., the slave address must be sent
with the direction bit set to 0. The next byte to be sent is
a command code, which, depending on the command,
may be followed by a command parameter. The DS2484
acknowledges valid command codes and expected/
valid command parameters. Additional bytes or invalid
command parameters are never acknowledged.
I2C Communication Examples
See Table 10 and Table 11 for the I2C communication
legend and data direction codes.
Table 10. I2C Communication—Legend
SYMBOL
S
DESCRIPTION
START Condition
AD, 0
Select DS2484 for Write Access
AD, 1
Select DS2484 for Read Access
Sr
Repeated START Condition
P
STOP Condition
A
Acknowledged
A\
Not Acknowledged
(Idle)
<byte>
DRST
SRP
Bus Not Busy
Transfer of One Byte
Command “Device Reset” (F0h)
Command “Set Read Pointer” (E1h)
WCFG
Command “Write Device Configuration” (D2h)
ADJP
Command “Adjust 1-Wire Port” C3h)
1WRS
Command “1-Wire Reset” (B4h)
1WSB
Command “1-Wire Single Bit” (87h)
1WWB
Command “1-Wire Write Byte” (A5h)
1WRB
Command “1-Wire Read Byte” (96h)
1WT
Command “1-Wire Triplet” (78h)
Table 11. Data Direction Codes
Reading from the DS2484
To read from the DS2484, the master must access the
device in read mode, i.e., the slave address must be sent
with the direction bit set to 1. The read pointer determines
the register that the master reads from. The master can
continue reading the same register over and over again,
without having to readdress the device, e.g., to watch
the 1WB changing from 1 to 0. To read from a different
register, the master must issue the Set Read Pointer command and then access the DS2484 again in read mode.
Master-to-Slave Slave-to-Master
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DS2484
Single-Channel 1-Wire Master
with Adjustable Timing and Sleep Mode
I2C Communication Examples (continued)
Device Reset (After Power-Up)
S
AD,0
A
DRST
A
Sr
AD,1
A
<byte>
A\
P
Activities that are underlined denote an optional read access to verify the success of the command.
Set Read Pointer (To Read from Another Register)
Case A: Valid Read Pointer Code
S
AD,0
A
SRP
A
C3h
A
P
C3h is the read pointer code for the Device Configuration register.
Case B: Invalid Read Pointer Code
S
AD,0
A
SRP
A
E5h
A\
P
E5h is an invalid read pointer code.
Write Device Configuration (Before Starting 1-Wire Activity)
Case A: 1-Wire Idle (1WB = 0)
S
AD,0
A
WCFG
A
<byte>
A
Sr
AD,1
A
<byte>
A\
P
Activities that are underlined denote an optional read access to verify the success of the command.
Case B: 1-Wire Busy (1WB = 1)
S
AD,0
A
WCFG
A\
P
The master should stop and restart as soon as the DS2484 does not acknowledge the command code.
Adjust 1-Wire Port (after power-up, e.g., to select a 1-Wire timing other than the default)
Case A: 1-Wire Idle (1WB = 0)
S
AD,0
A
ADJP
A
<byte>
A
<byte>
A
P
Repeat to set additional port parameters
The control byte is always acknowledged, regardless of its value. See the Adjust 1-Wire Port command description
for the format of the control byte.
Case B: 1-Wire Busy (1WB = 1)
S
AD,0
A
ADJP
A\
P
The master should stop and restart as soon as the DS2484 does not acknowledge the command code.
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22
DS2484
Single-Channel 1-Wire Master
with Adjustable Timing and Sleep Mode
I2C Communication Examples (continued)
Verifying the 1-Wire port configuration
The Adjust 1-Wire Port command sets the read pointer to the Port Configuration register. If other commands were
issued to the DS2484 since then, use the Set Read Pointer command first to position the read pointer to the Port
Configuration register.
Condition: 1-Wire Idle (1WB = 0), Read Pointer at Port Configuration Register
S
AD,1
A
<byte>
A
<byte>
A
<byte>
A\
P
Repeat to read additional port parameters
1-Wire Reset (To Begin or End 1-Wire Communication)
Case A: 1-Wire Idle (1WB = 0), No Busy Polling to Read the Result
S
AD,0
A
1WRS
A
P
(Idle)
S
AD,1
A
<byte>
A\
P
In the first cycle, the master sends the command. Then the master waits (Idle) for the 1-Wire reset to complete. In
the second cycle, the DS2484 is accessed to read the result of the 1-Wire reset from the Status register.
Case B: 1-Wire Idle (1WB = 0), Busy Polling Until the 1-Wire Command is Completed, then Read the Result
S
AD,0
A
1WRS
A
Sr
AD,1
A
<byte>
A
<byte>
A\
P
Repeat until the 1WB bit has changed to 0.
Case C: 1-Wire Busy (1WB = 1)
S
AD,0
A
1WRS
A\
P
The master should stop and restart as soon as the DS2484 does not acknowledge the command code.
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23
DS2484
Single-Channel 1-Wire Master
with Adjustable Timing and Sleep Mode
I2C Communication Examples (continued)
1-Wire Single Bit (To Generate a Single Time Slot on the 1-Wire Line)
Case A: 1-Wire Idle (1WB = 0), No Busy Polling
S
AD,0
A
1WSB
A
<byte>
A
P
(Idle)
S
AD,1
A
<byte>
A\
P
The idle time is needed for the 1-Wire function to complete. Then access the device in read mode to get the result
from the 1-Wire Single Bit command.
Case B: 1-Wire Idle (1WB = 0), Busy Polling Until the 1-Wire Command is Completed
S
AD,0
A
1WSB
A
<byte>
A
Sr
Repeat until the 1WB bit
has changed to 0.
AD,1
A
<byte>
A
<byte>
A\
P
When 1WB has changed from 1 to 0, the Status register holds the valid result of the 1-Wire Single Bit command.
Case C: 1-Wire Busy (1WB = 1)
S
AD,0
A
1WSB
A\
P
The master should stop and restart as soon as the DS2484 does not acknowledge the command code.
1-Wire Write Byte (To Send a Command Code or Data Byte to the 1-Wire Line)
Case A: 1-Wire Idle (1WB = 0), No Busy Polling
S
AD,0
A
1WWB
A
33h
A
P
(Idle)
33h is the valid 1-Wire ROM function command for Read ROM. The idle time is needed for the 1-Wire function to
complete. There is no data read back from the 1-Wire line with this command.
Case B: 1-Wire Idle (1WB = 0), Busy Polling Until the 1-Wire Command is Completed.
S
AD,0
A
1WWB
A
33h
A
Sr
Repeat until the 1WB bit
has changed to 0.
AD,1
A
<byte>
A
<byte>
A\
P
When 1WB has changed from 1 to 0, the 1-Wire Write Byte command is completed.
Case C: 1-Wire Busy (1WB = 1)
S
AD,0
A
1WWB
A\
P
The master should stop and restart as soon as the DS2484 does not acknowledge the command code.
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24
DS2484
Single-Channel 1-Wire Master
with Adjustable Timing and Sleep Mode
I2C Communication Examples (continued)
1-Wire Read Byte (To Read a Byte from the 1-Wire Line)
Case A: 1-Wire Idle (1WB = 0), No Busy Polling, Set Read Pointer After Idle Time
S
AD,0
A
1WRB
A
P
(Idle)
S
AD,0
A
SRP
A
E1h
A
Sr
AD,1
A
<byte>
A\
P
The idle time is needed for the 1-Wire function to complete. Then set the read pointer to the Read Data register
(code E1h) and access the device again to read the data byte that was obtained from the 1-Wire line.
Case B: 1-Wire Idle (1WB = 0), No Busy Polling, Set Read Pointer Before Idle Time
S
AD,0
A
1WRB
A
Sr
AD,0
A
SRP
A
E1h
A
(Idle)
S
AD,1
A
<byte>
A\
P
P
The read pointer is set to the Read Data register (code E1h) while the 1-Wire Read Byte command is still in progress. Then, after the 1-Wire function is completed, the device is accessed to read the data byte that was obtained
from the 1-Wire line.
Case C: 1-Wire Idle (1WB = 0), Busy Polling Until the 1-Wire Command is Completed
S
AD,0
A
Sr
1WRB
AD,0
A
A
Repeat until the 1WB bit
has changed to 0.
Sr
AD,1
A
<byte>
A
<byte>
A\
SRP
A
E1h
A
Sr
AD,1
A
<byte>
A\
P
Poll the Status segister until the 1WB bit has changed from 1 to 0. Then set the read pointer to the Read Data register (code E1h) and access the device again to read the data byte that was obtained from the 1-Wire line.
Case D: 1-Wire Busy (1WB = 1)
S
AD,0
A
1WRB
A\
P
The master should stop and restart as soon as the DS2484 does not acknowledge the command code.
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25
DS2484
Single-Channel 1-Wire Master
with Adjustable Timing and Sleep Mode
I2C Communication Examples (continued)
1-Wire Triplet (To Perform a Search ROM Function on 1-Wire Line)
Case A: 1-Wire Idle (1WB = 0), No Busy Polling
S
AD,0
A
1WT
A
<byte>
A
P
(Idle)
S
AD,1
A
<byte>
A\
P
The idle time is needed for the 1-Wire function to complete. Then access the device in read mode to get the result
from the 1-Wire Triplet command.
Case B: 1-Wire Idle (1WB = 0), Busy Polling Until the 1-Wire Command is Completed
S
AD,0
A
1WT
A
<byte>
A
Sr
Repeat until the 1WB bit
has changed to 0.
AD,1
A
<byte>
A
<byte>
A\
P
When 1WB has changed from 1 to 0, the Status register holds the valid result of the 1-Wire Triplet command.
Case C: 1-Wire Busy (1WB = 1)
S
AD,0
A
1WT
A\
P
The master should stop and restart as soon as the DS2484 does not acknowledge the command code.
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26
DS2484
Single-Channel 1-Wire Master
with Adjustable Timing and Sleep Mode
Applications Information
SDA and SCL Pullup Resistors
must not exceed 300ns. Assuming maximum rise time,
the maximum resistor value at any given capacitance CB
is calculated as: RP(MAX) = 300ns/(CB x ln(7/3)). For a
bus capacitance of 400pF, the maximum pullup resistor
would be 885I.
Pullup Resistor RP Sizing
Because an 885I pullup resistor, as would be required
to meet the rise time specification at 400pF bus capacitance, is lower than RP(MIN) at 5.5V, a different approach
is necessary. The “Maximum Load at Minimum RP Fast
Mode” line in Figure 10 is generated by first calculating
the minimum pullup resistor at any given operating voltage (“Minimum RP” line) and then calculating the respective bus capacitance that yields a 300ns rise time.
According to the I2C specification, a slave device must
be able to sink at least 3mA at a VOL of 0.4V. This DC
condition determines the minimum value of the pullup
resistor: RP(MIN) = (VCI2C - 0.4V)/3mA. With an I2C pullup voltage VCI2C of 5.5V, the minimum value for the pullup resistor is 1.7kI. The “Minimum RP” line in Figure 10
shows how the minimum pullup resistor changes with the
operating (pullup) voltage.
MINIMUM RP (Ω)
For I2C systems, the rise time and fall time are measured
from 30% to 70% of the pullup voltage. The maximum
bus capacitance, CB, is 400pF. The maximum rise time
Only for pullup voltages of 3V and lower can the maxi­
mum permissible 400pF bus capacitance be maintained.
A reduced 300pF bus capacitance is acceptable for 4V
and lower pullup voltages. For fast mode operation at
any pullup voltage, the bus capacitance must not exceed
200pF. The corresponding pullup resistor value at the
voltage is indicated by the “Minimum RP” line.
2000
500
1600
400
1200
300
MINIMUM RP
200
800
LOAD (pF)
SDA is an open-drain output on the DS2484 that requires
a pullup resistor to realize high-logic levels. Because the
DS2484 uses SCL only as input (no clock stretching), the
master can drive SCL either through an open-drain/collector output with a pullup resistor or a push-pull output.
MAXIMUM LOAD AT MINIMUM RP FAST MODE
400
100
0
0
1
2
3
4
5
PULLUP VOLTAGE (V)
Figure 10. I2C Fast Mode Pullup Resistor Selection Chart
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27
DS2484
Single-Channel 1-Wire Master
with Adjustable Timing and Sleep Mode
Package Information
Ordering Information
PART
TEMP RANGE
PIN-PACKAGE
DS2484R+T
-40NC to +85NC
6 SOT23 (3k pieces)
DS2484Q+T
-40NC to +85NC
8 TDFN-EP* (2.5k pieces)
+Denotes a lead(Pb)-free/RoHS-compliant package.
T = Tape and reel.
*EP = Exposed pad.
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a
“+”, “#”, or “-” in the package code indicates RoHS status only.
Package drawings may show a different suffix character, but the
drawing pertains to the package regardless of RoHS status.
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
6 SOT23
U6SN+1
21-0058
90-0175
8 TDFN-EP
T823+1
21-0174
90-0091
Maxim Integrated
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28
DS2484
Single-Channel 1-Wire Master
with Adjustable Timing and Sleep Mode
Revision History
REVISION
NUMBER
REVISION
DATE
0
5/13
DESCRIPTION
Initial release
PAGES
CHANGED
—
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent
licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and
max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000
www.BDTIC.com/maxim
© 2013 Maxim Integrated Products, Inc.
29
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.